i've done the elite 4 and caught myself the Mewto already, but now i was looking for the mega stone of alakazam Now i know it's in the reflection cave floor 3, now i went there and stood on the color circle there But i got no stone and i saw a picture of someone getting the stone there? i got pokemon X might ala be Y only?
Finisshed it yesterday! i had it a few days early! But now i'm stuck i was hunting for all the mega stone's after Elite 4, but i can't seem to find them and now i know i needed an ring upgrade ( forgot about that) i'm trying to find serena my rival but i can't find her in kiloud city! and i was at every city before i saw that post, so again going from city to city to find her ... xD
You must first complete a round in the battle mansion in kiloude city, then go up to the benches and she will be there. Afterwards she will tell you to go to anistar city to see the professor, he will be near the sun dile and then the mega ring will be upgraded so you can locate certain mega stones at night time between 8-9pm :) hope this helps.
Most of these are available after you beat your rival. (You have to be postgame, meaning after finishing Elite Four, go to Kiloud city via the station in Lumiose City after getting the pass from your professor - and fight 8 or 9 rounds in the Battle Maison in Kiloud City and your rival will appear up top of the city, near on a bench.)